1. Field of the Invention
The present invention relates to a setting tool for driving nail-shaped fastening elements in a hard constructional component and including a housing, a guide cylinder, a drive piston axially displaceable in the guide cylinder and having a stem and a head, and a resetting element pivotable about an axle supported in the housing and having a lever arm cooperating with a front, in a setting direction, surface of the drive piston head.
2. Description of the Prior Art
At present, setting tools, e.g., explosive powder charge operated setting tools are used for driving nail-shaped fastening elements in a hard constructional component, such as concrete, stone of steel. Such setting tool is disclosed in German Publication No. 1,812,207. The setting tool disclosed in this publication includes a housing, a guide cylinder at least partially located in the housing, and a drive piston axially displaceable in the guide cylinder for driving in fastening elements. After each setting process, the drive piston is return to its initial position by a resetting element which is pivotally supported in the housing. The resetting element projects through a side opening in the guide cylinder into the interior of the guide cylinder and cooperates there with a front, in the setting direction, end surface of the drive piston head. The resetting element is pivotally supported by axle which projects through an opening formed in the housing and which extends perpendicular to the setting direction. The resetting element cooperates with a pressure spring supported against the housing and a stop surface of the resetting element which faces in the setting direction.
In each setting process, the drive piston is displaced in the setting direction with a very high speed. The high speed of the drive piston results in extremely high accelerations and loads applied at least to a section of the resetting element which engages the front end surface of the drive piston head. Because of its large length, the resetting element has a big mass, which results in large vibrations of the entire setting tool each time the resetting element runs on a stop limiting the displacement of the resetting element in the setting direction. Though the stop in formed of a material having damping characteristics, only a small portion of the kinetic energy of the resetting element is damped. Therefore, an early wear and damage of all involved parts of the setting tool cannot be prevented.
Accordingly, an object of the present invention is to provide a reliable and easily operable setting tool having a resetting element with a very high service life.